Thermally activated calibration system for chemical sensors

ABSTRACT

A device for remotely calibrating leak sensors. A supply of liquid analyte calibrant is stored in a reservoir, and is communicated to an outlet nozzle by a conduit having a throughbore. The conduit terminates in an outlet nozzle, and portion of the conduit defines a dosing chamber for storing a measured dose of the liquid calibrant. A thermal activator such as a resistive coil or a radio frequency unit is disposed adjacent the dosing chamber for applying a steep thermal gradient in order to bring the calibrant quickly to its boiling point such that the measured quantity is ejected from the outlet nozzle.

FIELD OF THE INVENTION

The present invention relates to a calibration system for chemicalsensors. More specifically, the present invention relates to a thermallyactuated calibration device which delivers a metered dose of calibrantfrom a dosing chamber.

BACKGROUND OF THE INVENTION

Industrial manufacturing, processing and storage facilities such aschemical plants, refineries and shipping terminals typically include avast network of piping systems for transporting the raw or finishedproducts through the facility. Such piping systems necessarily include anumber of valves for controlling the flow of material through thefacility.

Many of the products handled in the aforementioned plants are hazardousvolatile organic compounds (VOC's). Unfortunately, the valves used tocontrol the flow of material through the plants typically experience acertain amount of undesired leakage referred to as "fugitive" emissions.Fugitive emissions, which are regulated by the Environmental ProtectionAgency (EPA), frequently occur around the packing between the valve stemand the body of the valve. These fugitive emissions must be monitored inorder to comply with EPA emission regulations. Accordingly, leakdetectors are placed near the valves, usually adjacent to the leak pronevalve stems or other non-point sources, in order to monitor the leakagerate.

In order to obtain accurate readings, the leak detectors must becalibrated on a periodic basis, which typically must be accomplishedfrom a remote location. One method of calibrating such leak detectors isto eject a small quantity of calibrant adjacent to the leak detector.The detector reading is then compared to a standard based on empiricaldata or a look up table, and the detector is adjusted accordingly.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a leak sensorcalibration device includes a reservoir for storing a liquid analytecalibrant. A conduit is in flow communication with the reservoir, and aportion of the conduit defines a dosing chamber for storing a preciselymeasured quantity of the calibrant. An outlet nozzle, which is typicallylocated closely adjacent to the leak sensor to be calibrated, is in flowcommunication with the dosing chamber. A thermal activator, preferably aresistive coil or radio frequency unit capable of applying a steepthermal gradient, surrounds the dosing chamber. Upon energizing thethermal activator, the measured quantity of calibrant stored in thedosing chamber is ejected through the outlet nozzle. The leak sensor isthen calibrated by comparing the actual reading to a standard formulabased on empirical data.

In further accordance with the preferred embodiment, the device includesa first remotely operated valve at the outlet nozzle and a secondremotely operated valve between the reservoir and the dosing chamber.The valves prevent inertial dispersion of the calibrant under seismicconditions, and also prevent free surface evaporation. The outlet valveand nozzle ideally are located higher than the second valve, which keepsthe calibrant out of contact with the soft rubber, Viton coated valveseat, thus preventing "off-gassing." When the thermal activator isenergized by a control system, the control system opens the outlet valveand closes the valve between the dosing chamber and the reservoir, whichprevents calibrant from flowing back to the reservoir. The thermalactivator is preferably capable of bringing the calibrant within thedosing chamber to its boiling point in about 10 milliseconds.

In accordance with another aspect of the invention, a device fordelivering a metered quantity of vaporized liquid material to thesurrounding atmosphere includes a storage reservoir and a conduit inflow communication with the reservoir. A portion of the conduit definesa dosing chamber for storing a metered quantity of the liquid material.The portion of conduit between the reservoir and the dosing chamberincludes an impeding portion for restricting the flow of the liquidmaterial from the dosing chamber back to the reservoir. The end of theconduit defines outlet nozzle in flow communication with the dosingchamber, and a thermal activator adjacent the dosing chamber applies asteep thermal gradient which vaporizes the liquid material in the dosingchamber thereby ejecting the vaporized material through the outletnozzle to the atmosphere.

In accordance with yet another aspect of the invention, a remotelyoperable calibrating device includes a reservoir for storing a supply ofliquid calibrant, and has a conduit in flow communication with thestorage reservoir. The conduit terminates in an outlet nozzle and has acentral portion defining a dosing chamber which stores a measuredquantity of the liquid calibrant. A thermal activator is used to heatthe liquid calibrant in the dosing chamber to its boiling point. A valveisolates the outlet nozzle from the surrounding atmosphere when thethermal activator is inactive, and when the thermal activator isenergized the valve system isolates the dosing chamber from thereservoir, thus preventing liquid in the dosing chamber from beingrouted back into the reservoir. A remotely operable control system isconnected to the valve system and the thermal activator for controllingthe operation of the device.

Further advantages and features of the present invention will becomeevident to those skilled in the art upon a reading of the followingdescription.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic view, partly in section, of the leak sensorcalibrating device according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The embodiment described herein is not intended to limit the inventionto precise form disclosed. Rather, the embodiment has been chosen anddescribed in order to enable those skilled in the art to follow theteachings of the present invention.

Referring now to the drawing, a calibration device incorporating thefeatures of the present invention is generally referred to by thereference numeral 10. Device 10 is typically placed closely adjacent toa leak detector or sensor (not shown), which in turn is typically placedclosely adjacent to the system which is to be monitored for leakage,such as a valve, a pipe system or seal, or other non-point emissionsource (not shown). Device 10 includes a reservoir 12 which contains aquantity of liquid analyte calibrant 14, which is preferably the samematerial as is running through the valve to be monitored.

Device 10 includes a conduit 16 which extends between the reservoir 12and an outlet nozzle 18. Conduit 16 includes a bore 20 extendingtherethrough. Conduit 16 further includes an intermediate or centralportion 22, a portion of which defines a dosing chamber 24. Dosingchamber 24 is preferably of predetermined volume, which for purposes ofthe preferred embodiment is in the range of 2 microliters (2×10⁻⁶ cubiccentimeters). Conduit 16 is preferably constructed of stainless steeltubing having an inside diameter of 0.008 inches and an outside diameterof 0.050 inches, or any other suitable thickwall small diameter tubing.A thermal activator 26, which is preferably a resistive coil or a radiofrequency heating unit, surrounds the conduit 16 adjacent the dosingchamber 24, enabling the activator 26 to heat a measured quantity 28 ofcalibrant 14 contained within the dosing chamber 24. The measuredquantity 28 is preferably determined by the internal volume of thedosing chamber 24, such that the proper measured quantity 28 is presentupon the dosing chamber being filled with calibrant 14. Alternatively,the measured quantity 28 may be determined by metering the flow ofcalibrant 14 into the dosing chamber 24 using known methods. The thermalactivator 26 is preferably capable of bringing the measured quantity 28contained within the dosing chamber 24 to its boiling point veryquickly, as in the range of about 10 milliseconds.

An outlet valve 30 having a magnetically coupled actuator 31 is locatedat outlet nozzle 18, and is shiftable between an open position in whichthe bore 20 (and dosing chamber 24) are in flow communication with thesurrounding atmosphere, and a closed position in which the bore 20 (anddosing chamber 24) are isolated from the surrounding atmosphere. Asecond valve 32 having a magnetically coupled actuator 33 is disposedalong conduit 16 between dosing chamber 24 and reservoir 12. Valve 32 isshiftable between an open position in which dosing chamber 24 is in flowcommunication with reservoir 12, and a closed position in which thedosing chamber 24 is isolated from the reservoir 12. Preferably, each ofvalves 30, 32 are remotely operable from a common control system 34.Control system 34 is also used to energize the thermal activator 26 aswill be discussed in greater detail below. Further, the pneumaticimpedance through valve 30 is preferably about fifty (50) times greaterthan the pneumatic impedance through valve 32, the importance of whichwill be discussed in greater detail below.

The elevation of the outlet nozzle 18 and associated valve 30 is higherthen elevation of valve 32. Thus, if valve 32 does not close completely,the liquid analyte 14 is kept out of contact with the seat of valve 30.Valve 30 preferably includes a chemically resistant soft rubber seat,such as a material sold under the tradename Viton, and is coated withTeflon. The Teflon coating prevents calibrant absorption into the Vitonseat, thus preventing "off-gassing". The closure force of valve 30 maybe relatively low, such as in the range of 25 psi of closure force onnozzle 18.

In operation, when the device 10 is inactive, valve 30 is closed, valve32 is open, and the calibrant 14 in reservoir 12 is free to flow intothe dosing chamber 24. When it is desired to activate the device 10,control system 34 closes valve 32, thus seriously impeding or preventingflow between the dosing chamber 24 and the reservoir 12, and thermalactivator 26 is energized. Simultaneously, or shortly thereafter, valve30 is opened. The now vaporized calibrant 14 contained within dosingchamber 24 is at its boiling point, and is ejected through the opennozzle 18. At that point, the exhausted calibrant can be mixed with aknown quantity of atmosphere from around a valve for measuring orpredicting its leak emissions. The leak sensor (not shown) can becalibrated by comparing the obtained sensor reading to empirical data,or by using other known methods.

Alternatively, the impedance between the dosing chamber 24 and thereservoir 12 may be achieved using a mechanical restriction rather thana closeable valve. Also, in less severe environments or in environmentswhere inertial dispersion of calibrant is not expected, it isconceivable that surface tension and pneumatic impedance may besufficient to prevent evaporation as well as backward flow of thecalibrant, thus making it possible to dispense with one or both of thevalves.

It will be understood that the above description does not limit theinvention to the above-given details. It is contemplated that variousmodifications and substitutions can be made without departing from thespirit and scope of the following claims.

What is claimed:
 1. A leak sensor calibration device, comprising:a reservoir for storing a liquid calibrant; a conduit in flow communication with the reservoir, a portion of the conduit defining a dosing chamber for storing a measured quantity of the calibrant; an outlet nozzle in flow communication with the dosing chamber; and a thermal activator adjacent the dosing chamber for vaporizing the measured quantity of calibrant in the dosing chamber and ejecting the measured quantity through the outlet nozzle.
 2. The device of claim 1, including a remotely operated valve at the outlet nozzle, the valve being shiftable between a closed position wherein the dosing chamber is isolated from the surrounding atmosphere to an open position wherein the dosing chamber is in flow communication with the surrounding atmosphere.
 3. The device of claim 1, including a remotely operated valve disposed between the reservoir and the dosing chamber, the valve being shiftable between a closed position wherein the reservoir is isolated from the dosing chamber and an open position wherein the reservoir is in flow communication with the dosing chamber for filling the dosing chamber with the calibrant.
 4. The device of claim 1, including first and second remotely operated valves, the first valve being located at the outlet nozzle, the first valve being shiftable between a closed position wherein the dosing chamber is isolated from the surrounding atmosphere to an open position wherein the dosing chamber is in flow communication with the atmosphere, the second valve being disposed between the reservoir and the dosing chamber, the second valve being shiftable between a closed position wherein the reservoir is isolated from the dosing chamber and an open position wherein the reservoir is in flow communication with the dosing chamber.
 5. The device of claim 4, wherein the valves are electrically operated, and further including a control system for remotely operating the valves and for energizing the thermal activator.
 6. The device of claim 5, wherein the control system maintains the second valve in the closed position and the first valve in the open position when the activator is energized.
 7. The device of claim 1, wherein the thermal activator is a resistive coil.
 8. The device of claim 1, wherein the thermal activator is a radio frequency unit.
 9. The device of claim 1, wherein the thermal activator supplies a thermal gradient sufficient to vaporize the calibrant in the dosing chamber in about 10 milliseconds.
 10. A leak sensor calibrating device, comprising:a reservoir for storing a liquid calibrant; a conduit in flow communication with the storage reservoir, the conduit terminating in an outlet nozzle and having a central portion defining a dosing chamber for storing a measured quantity of the liquid calibrant; a thermal activator for heating the measured quantity of liquid calibrant in the dosing chamber; a valve system for isolating the outlet nozzle from the surrounding atmosphere when the thermal activator is inactive and further for isolating the dosing chamber from the reservoir when the thermal activator is active; and a control system operatively connected to the valve system and the thermal activator.
 11. A leak sensor calibration device for injecting a metered quantity of vaporized liquid material in the vicinity of a leak sensor, the device comprising:a reservoir for storing the liquid material; a conduit in flow communication with the reservoir, a portion of the conduit defining a dosing chamber for storing the metered quantity of the liquid material, the conduit further including an impeding portion for restricting the flow of the liquid material from the dosing chamber back to the reservoir; an outlet nozzle in flow communication with the dosing chamber; and a thermal activator adjacent the dosing chamber for vaporizing the liquid material in the dosing chamber thereby ejecting the vaporized material through the outlet nozzle to the atmosphere.
 12. The device of claim 11, wherein the impeding portion is a remotely operated valve disposed between the reservoir and the dosing chamber, the valve being shiftable between a closed position wherein the reservoir is isolated from the dosing chamber and an open position wherein the reservoir is in flow communication with the dosing chamber.
 13. The device of claim 12, wherein the valve is remotely operable.
 14. The device of claim 11, including a remotely operated outlet valve at the outlet nozzle, the valve being shiftable between a closed position wherein the dosing chamber is isolated from the surrounding atmosphere to an open position wherein the dosing chamber is in flow communication with the surrounding atmosphere.
 15. The device of claim 11, including an first valve at the outlet nozzle and wherein the impeding portion includes a second valve, each of the valves being remotely operable, the first valve being shiftable between a closed position wherein the dosing chamber is isolated from the surrounding atmosphere to an open position wherein the dosing chamber is in flow communication with the atmosphere, the second valve being disposed between the reservoir and the dosing chamber, the second valve being shiftable between a closed position wherein the reservoir is isolated from the dosing chamber and an open position wherein the reservoir is in flow communication with the dosing chamber.
 16. The device of claim 15, wherein the valves are electrically operated, and further including a control system for controlling the valves and for energizing the thermal activator.
 17. The device of claim 16, wherein the control system maintains the second valve in the closed position and the first valve in the open position when the activator is energized.
 18. The device of claim 11, wherein the elevation of the outlet is disposed above the elevation of the impeding portion.
 19. The device of claim 11, wherein the pneumatic impedance through the impeding portion is about fifty times greater than the pneumatic impedance through the outlet nozzle.
 20. The device of claim 11, wherein the volume of the dosing chamber is about 2×10⁻⁶ liters. 